X-ray tube



56 5'; s, 1936. L. F. EHRKE v 4 2,053,327

I X-RAY TUBE Filed Nov. 22, 1934 INVENTOR A [HP/ff ATTORN EY PatentedSept. 8, 1936 UNITED STATES PATENT orrlca X-RAY TUBE PennsylvaniaApplication November 22, 1934, Serial No. 754,231

Claims.

My invention relates to X-ray devices and comprises in particular a newX-ray anode or target which is particularly adapted for use inconnection with the continuous generation of X-rays,

5 for example, in the administration of therapeutic treatments.

In the usual construction of such X-ray tubes it is customary to providea surface of a refractory metal, such as tungsten or the like,molecularly secured to a stem of good heat conducting metal, such ascopper. During operation of the tube the electron stream flowing fromthe thermionic cathode is more or less concentrated upon the refractorymetal surface resulting in the generation of X-rays as well asconsiderable heat which is transmitted to the anode stem. The highpotential electrical energy for the tube is usually supplied from a hightension sourceand either rectified by the X-ray tube itself or byintermittent direct current by the utilization of a separate rectifier.Accordingly the anode surface or target is subjected to severemechanical shocks caused by the'intermittent bombardment thereofaccompanied by periods of intense heating followed by intervals ofcooling which has a tendency to cause cracking or tearing of therefractory metal target. as well as a buckling away from the back plateor anode stem.

It is accordingly customary to obviate undue heatingof; the anode inX-ray tubes, when employedfor therapeutic treatments or other conditionsrequiring a heavy load, to circulate a cooling and insulatingmaterialthrough the hollow anode stem in an endeavor to maintain an eventemperature.

If water is employed the device cannot be advantageously renderedshockproof because of the high voltages-to which the tube is subject-edand the fact that water is not dependable as a dielectric medium and maythustransmit the high electrical potential applied to the anode to otherportions of the apparatus with resulting shocks to a patient oroperator.

As a consequence it is expedient to utilize a high'dielectric fluid,such as hydrocarbon oils, but such fluids also have a disadvantageousfeature in that after continued use of the tube its cooling .efliciencyis considerably decreased. The apparent reason for this decreasedeficiency resides in a cracking of the oil and the accumulation of acarbonaceous deposit on the interior surface of the hollow anode,particularly at the points of greatest heat concentration. This crackingof the oil may to some extent be promoted by the copper per se or anycopper oxide which may be contained on the'interior surface of the anodeand the carbonaceous deposit thus formed, because it has a low heatconductivity characteristic, acts after a short time as a heat insulatorbetween the anode stem and the cool ing and insulating material.

It is accordingly an object of my present invention to provide an X-raytube suitable for continuous operation wherein an anode is provided.through which a cooling and insulating material, such as oil circulatesand the possibility of a carbonaceous deposit being formed thereonresulting in a decrease in the efficiency of the heat transfer isobviated.

Another object of my present invention is the provision of an X-ray tubehaving an anode which becomes heated'during operation of the tube'andwherein a cooling and insulating me-- dium is caused to circulatetherethrough with the interior surface of the hollow anode being soconstructed that any carbonaceous products which deposit thereon due todecomposition of the cooling and insulating medium will not betenaciously held thereby.

A further object of my present invention is the provision of an X-raytube having an anode which becomes heated duringoperation of the tubeand wherein a cooling and insulating material is arranged to circulatethrough the hollow anode stem for the purpose of transmitting the heatfrom the points of greatest heat concentration to the cooling andinsulating medium and the hollow anode stem is provided with a coatingof a material difierent'from that of the anode stem which has aninappreciable afiinity for any carbonaceous deposits that may be formeddue to cracking of the cooling and insulating material upon successivesubjection to high temperature thus enabling a free circulation of themedium ov-era long period of time.

Still further objects of my present invention become obvious to thoseskilled in the art by reference to the accompanying drawing wherein,

Figure 1 is a side view of an X-ray tube constructed in accordance withmy present invention. I

Fig. 2 is a sectional view on an enlarged scale of the anodeconstruction of the tube shown in Fig. 1 with a portion thereof brokenaway, and

Fig. 3 is a sectional view in elevation also on an enlarged scale andtaken on the line IIIIII of Fig. 1.

Referring now to the drawing in detail I have shown in Fig. l asubstantially cylindrical evacuated envelope 5 which may be of uniformdiameter or have a portion thereof in the vicinity of the cathodeelectrode of slightly less diameter for the conservation of space inactual use of the tube. The envelope is provided at one end thereof witha reentrant sleeve portion 6 to which is sealed in a manner well knownto the art a cathode electrode shown generally at I. This electrode isprovided with .a metallic focusing cup .8 having recessed thereinafilamentary cathode 9 in accordance with the usual construction. Thethermionic cathode 9 is arranged to receive heating current from asuitable source of supply through a pair of conductors II] and I2 aswell as being connected to one side of a high voltage source of supply(not shown).

The opposite end of the envelope 5 is similarly provided with areentrant sleeve portion I3 to which is appropriately sealed, such as bya feather edge copper annulus I4 (Fig. 2), an anode .electrode I5provided with a refractory metal target I6, of tungsten, thorium .or thelike, and having a recess I'I extending longitudinally thereof whichterminates at the head of the anode immediately in back of the targetIS. The anode I5 may be supplied with a potential from the high Voltagesource of supply by means of a conductor 18 and the same may be cooledduring operation of the tube by the circulation of a cooling mediuminteriorly of the hollow anode I 5 by the provision of concentricinsulated conduits I9 and 20. Upon incandescence of the thermioniccathode 9 and the application of a high potential between the electrodesI and I5 electrons will flow from the thermionic cathode 9 and bombardthe target It with the accompanying generation of X-rays.

In order to prevent any scattered or secondary electrons from the anodefrom impinging upon the glass walls of the envelope a sleeve 22 maybeprovided which forms an integral part of the envelope by being sealedthereto at a point well behind the seal of the anode to the reentrantsleeve I3. This sleeve and its operation form no part per se of mypresent invention, but is shown and described more in detail in thecopending application of C. M. Slack, Serial No. 750,633 filed October30, 1934 and assigned to the same assignee as the present invention. Inview thereof further description herein is deemed unnecessary.

The hollow anode I5 is adapted to be threadedly engaged by the outerinsulated conduit I9 and the inner concentric conduit 20 extendslongitudinally of the hollow anode well within the same to a pointadjacent the rear surface immediately in back of the refractory metaltarget I6. During operation of the tube the cooling and insulatingmedium, such as a hydrocarbon oil, is arranged to circulate from asuitable reservoir (not shown) and enters the hollow anode I5 throughthe inner concentric conduit 20, where it discharges into the latter atthe point of greatest heat concentration, namely, at the surface thereofimmediately in back of the refractory metal target I6. After contactingthe heated surfaces of the anode stem it flows through the outerconcentric conduit I9 back to the reservoir to be cooled and Due to theintense heat again repeat the cycle. of the anode I 5, and particularlyat the point immediately in back of the refractory metal target, acracking of the cooling and insulating medium frequently results and acarbonaceous deposit will accumulate not only at the point of greatestheat concentration, as before noted, but also over the remaining innersurface of the hollow anode.

Th formation of this deposit in addition to being attributable to theintense heat causing cracking of the hydrocarbon oil may to some extentbe attributable to the copper per se or to the copper oxide formedthereon, and upon continued use of the tube with a resultingaccumulation of carbonaceous deposit the latter eventually acts as aheat insulator due to its low heat conductivity characteristic, thusdecreasing the efficiency of heat transfer.

"In order to prevent accumulation of this deposit I provide theinnermost surface of the hollow anode with a layer of metal 24 ofdifferent composition than the anode, such as mirrorlike or highlypolished chromium, nickel or the like, which .has an inappreciableaffinity for any carbonaceous deposit which may be formed upon crackingof the cooling and insulating medium. While this layer of metal 24 in noway precludes sacracking of the oil, due to the high temperature towhich the same is subjected, nevertheless because of its highly polishedsurface as well as its inappreciable affinity to carbonaceous deposits,the same if formed will not be tenaciously held by this layer of metal.This accordingly results in .aneflicient transfer of the heat from theanode stem to the cooling and insulating material even after long andcontinued use of the X-ray tube and maintains the efiiciency .of theheat transfer substantially the same as when the tube is first employed.

As a modification of my present invention I may utilize together withthe cooling and insulating material, such as the hydrocarbon oils beforementioned, a liquid which has the property of removing any carbonaceousdeposit from the interior surface of the anode, such for example asliquids generally termed carbon solvents.

As a still further precautionary measure I may utilize at some point inthe circulatory system for the anode a suitable filter which, whilepermitting. free circulation of the cooling medium neverthelessfunctions to accumulate any of the carbonaceous deposit resulting from acracking of the oil, and thus prevents circulation of this carbonaceousdeposit through the circulatory system, with the usual result of itaccumulating at the points of greatest heat concentration and causing adecrease in the efliciency of heat transfer.

It thus becomes obvious to those skilled in the art that I have providedan electron discharge tube, such for example as an X-ray tube, which maybe operated in connection with the continuous generation of X-rays overlong periods of time, as in the administration of therapeutictreatments, and wherein a carbonaceous deposit is prevented fromaccumulating at the points of greatest heat concentration interiorly ofthe hollow anode. Inasmuch as such deposit, which would ordinarilyfunction as a heat insulator, is prevented from being formed at thepoints of greatest heat concentration the efficiency of the heattransfer from the highly heated points of the anode electrode to the oilis maintained over a long period of continued use of the tube.

Although I have shown and described several embodiments of my presentinvention I do not desire to be limited thereto as various othermodifications of the same may be made without departing from the spiritand scope of the appended claims.

What is claimed:

1. An X-ray tube comprising an envelope, a cathode, an anode including arefractory-metal target which becomes heated during operation byelectron bombardment and a hollow anode stem, and means disposed on theinterior surface of said anode stem consisting of a material differingfrom that of said hollow anode stem and having a highly polished surfaceoffering an inappreciable resistance to the circulation of a cooling andinsulating material to prevent the accumulation of carbonaceous depositsinteriorly of said hollow anode stem.

2. An X-ray tube comprising an envelope, a thermionic cathode, an anodeincluding a refractory metal target which becomes heated duringoperation by electron bombardment and a hollow anode stem, means forcirculating a cooling and insulating material through said hollow anodestem for transferring heat from said anode, and means disposed on theinterior surface of said anode stem having surface characteristics whichoffer an inappreciable affinity for any carbonaceous deposit formed bysaid cooling and insulating material and presenting substantially noresistance to the flow thereof.

3 An X-ray tube comprising an envelope, a thermionic cathode, an anodeincluding a refractory metal target which becomes heated duringoperation by electron bombardment and a hollow anode stem, means forcirculating a cooling and insulating material through said hollow anodestem for transferring heat from said anode, and means disposed on theinterior surface of said anode having a surface which preventscarbonaceous deposits from tenaciously adhering thereto whereby theefficiency of heat transfer from said hollow anode to said cooling andinsulating material is not impaired after long continued use of saidX-ray tube.

4. An X-ray tube comprising an envelope, a

thermionic cathode, an anode including a refractory metal target whichbecomes heated during operation by electron bombardment and a hollowmetallic anode stem, means for circulating a cooling and insulatingmaterial through said hollow metallic anode stem for transferring heatfrom said anode to said cooling and insulating material, and a metalliccoating of a material differing from that of said anode stem disposedupon the interior surface of the latter and having surfacecharacteristics offering an inappreciable afiinity for any carbonaceousdeposit formed by said cooling and insulating material and offeringsubstantially no resistance to the flow thereof.

5. An X-ray tube comprising an envelope, at thermionic cathode, an anodeincluding a refractory metal target which becomes heated duringoperation by electron bombardment and a hollow metallic anode stern,means for circulating a cooling and insulating material through saidhollow metallic anode stern for transferring heat from said anode tosaid cooling and insulating material, and a metallic coating of a metaldiffering from that of said anode'stem disposed upon the interiorsurface of the latter and provided with a highly polished surface toprevent carbonaceous deposits tenaciously adhering thereto upon crackingof said cooling and insulating material when subjected to heat from saidhollow anode thus maintaining the efficiency of heat transfer from saidhollow anode stem to said cooling and insulating material after longcontinued use of said X-ray tube.

LOUIS F. EHRKE.

